Wireless communication systems may operate using fixed infrastructure equipment or in ad-hoc configurations. In fixed infrastructure models, wireless communication systems typically comprise a plurality of base stations and mobile stations that communicate using an over-the-air communication protocol using physical layer technologies such as Code Division Multiple Access (CDMA) technology. IS-95, Mobile Station-Base Station Compatibility Standard for Dual-Mode Wideband Spread Spectrum Cellular System, published in July 1993 is an example of such a protocol standard. CDMA uses digital spread spectrum techniques that are less susceptible to interference.
Wireless communications systems such as CDMA typically operate using a variety of channels. In CDMA, for example, channelization is accomplished using orthogonal or quasi-orthogonal codes. Different channels generally have different purposes. Common channels are used to communicate to a plurality of mobile stations or base stations at the same time while dedicated channels are typically used for communication to and from one mobile station.
Pilot channels are channels that are typically receivable by a plurality of mobile stations for use in pilot set maintenance (selection of serving sector(s)) and coherent demodulation. Pilot channels can also be used for timing and phase measurements for geo-location purposes.
Wireless communication systems are beginning to incorporate network-based and network-assisted location determination systems. Some wireless handsets have network assisted GPS capability, some have Forward Link Trilateration capabilities, while others have hybrid capabilities that may use multiple technologies. Some CDMA wireless handsets make use of the wireless communication signals themselves to perform location-related measurements such as in Enhanced Forward Link Trilateration (EFLT) or Advanced Forward Link Trilateration (AFLT) methods that use the difference in phase delays of wireless signals as input to location calculations. Other wireless communication systems, such as some telematics products incorporate stand-alone capabilities such as GPS. An example of a hybrid system is one in which a mobile station has assisted-GPS receiver capabilities and AFLT measurement capabilities.
Location information can be used to enable location-based services. Similarly, location-based services can be network or terminal based or distributed between wireless communication system entities. Distributed or network based services generally require active communication and use of wireless resources such as communication channels. For example, the TIA/EIA location protocol standard IS-801 enables network-assisted GPS via messaging over the CDMA wireless link between infrastructure and terminals. Such resources may be expensive, limited and have quality of service impacts on usage such as moderate or high latency.
Hybrid systems such as terminals with assisted-GPS (AGPS) and AFLT capability may use measurements from both GPS and AFLT in combination to solve for the terminal position. Typically the uncertainty in the GPS and AFLT measurements may be different and thus, for best results, the measurements should be weighted inversely proportional to the uncertainty of the measurement. For example, if for a certain terminal at a certain time, the AFLT measurements have greater uncertainty than the GPS phase measurements then the GPS measurements may be given more importance (weight) in the computation of the terminal location solution.
What is needed is a system that measures pilot phase root mean square error for the purpose of determining how much relative importance to give individual measurements relative to each other and relative to other technologies such as GPS.
The IS-801 standard supports communication of pilot phase measurements with RMSE (root mean square error) estimates and hybrid systems call for reliable uncertainty (RMSE) estimates. Currently known methods use the energy of the pilot to estimate RMSE or the age of the measurement. The older the measurement the larger the RMSE, and similarly, typically the weaker the pilot strength, the larger the RMSE.
What is needed is a system which more accurately computes the RMSE for use in position location or any other applications.